<template>
    <ul class="list">
        <li class="item" 
        v-for="item of letters" 
        :key="item"
        :ref="item"
        @click="handleLetterClick"
        @touchstart="handleTouchStart"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd">{{ item }}</li>
    </ul>
</template>

<script>
export default {
    name: 'CityAlphabet',
    props:{
        cities: Object
    },
    computed: {
        letters() {
            const letters = []
            for (let i in this.cities){
                letters.push(i)
            }
            return letters
        }
    },
    data () {
        return {
            touchStatus : false,
            startY : 0,
            time :null
        }
    },
    updated () {
        this.startY = this.$refs['A'][0].offsetTop
    },
    methods:{
        handleLetterClick (e){
            this.$emit('change',e.target.innerText)
        },
        handleTouchStart () {
            this.touchStatus = true
        },
        handleTouchMove (e) {
            if(this.touchStatus){
                if(this.timer){
                    clearTimeout(this.time)
                }
                this.timer = setTimeout(()=>{
                    const touchY = e.touches[0].clientY - 79
                    const index = Math.floor((touchY - this.startY) / 20)
                    if(index>=0 && index < this.letters.length)
                        this.$emit('change',this.letters[index])
                },16)
                
            }
        },
        handleTouchEnd () {
            this.touchStatus = false
        }
    }
}
</script>

<style lang="stylus" scoped>
    @import '~styles/varibles.styl'
    .list
      display flex
      flex-direction column
      justify-content center
      position absolute
      right 0
      top 1.58rem
      bottom 0
      width .4rem
      .item
        line-height .4rem
        text-align center
        color $bgColor
</style>
